1. Field of the Invention
This invention relates to stabilization of laser output intensity, and, in particular, to a device for controlling the output of a semiconductor laser using a counter.
2. Description of the Prior Art
In a laser printer, a semiconductor laser is often used as a light beam source, and a laser beam emitted from the semiconductor laser is modulated in accordance with image information. The thus modulated laser beam is then deflected by a rotating deflector repetitively so that the deflected laser beam carrying image information is scanned along a predetermined imaginary scanning line repetitively across the surface of a travelling photosensitive member so that there is formed an electrostatic latent image in accordance with the image information. However, since the intensity of the laser beam output from the semiconductor laser is very sensitive to the operating temperature, there must be provided a control device for controlling the intensity of the laser output beam if the surrounding temperature varies.
One approach to control the output intensity of a semiconductor laser uses a counter, in which case, driver current is supplied to the semiconductor laser according to the count of the counter. The counter is normally maintained disabled to hold the current count, and when no recording operation takes place, the counter is enabled and the number of clock pulses is counted such that the output intensity of the semiconductor laser is at a reference value, thereby carrying out the setting of the output intensity of the semiconductor laser. And, then, the counter is again disabled. On the other hand, the photosensitive member used as an imaging member for forming thereon an image tends to deterioriate if the laser beam output from the semiconductor laser impinges on the photosensitive member while it is motionless, e.g., in a stand-by mode.